Passive smoking may cause twofold increases in risk of lung cancer in nonsmokers. Domestic radon daughters may be responsible for 20% of lung cancer in nonsmokers, at average exposure levels for the population. Over large regions of North America, 10 to 20% of the population may be exposed to radon at levels many times above average. Major social programs to ameliorate radon levels have been proposed in both Canada and the United States. Conflicting results concerning the form of the interactions between cigarette smoking and radon daughters have been obtained in the several published studies. Multiplicative interactions will affect risk estimates for both passive smoking and radon exposure for large segments of the population in a major way. The aim of this study is to quantify effects of passive smoking on uptake and retention of radon daughters in humans under the conditions of normal domestic exposures. Interactions of cigarette smoke with radon daughters have been ignored in studies of passive smoking. These interactions have two distinct components: (1) at the level of exposure and dose of radon daughters, and (2) at the level of carcinogenic effects. This proposal is aimed at the first of these components. An exploratory, descriptive field investigation of body contents of radon daughters in normal adult subjects, measured at their homes following their accustomed activity patterns, will be carried out. Radon daughter burdens will be related to passive smoking. Concurrent measurements of radon, radon daughters (and therefore working level ratios), and of atmospheric particle counts and size distributions will be made in the home. Smoking and physical activity patterns within the home will be correlated with the physical measurements. The study will be designed to compare passive smokers with nonsmokers not exposed to passive smoking, and with active smokers.